PDFSIDER is a newly identified malware variant that utilizes DLL side-loading to deploy a covert backdoor with encrypted command-and-control capabilities. It exploits vulnerabilities in legitimate software like PDF24 Creator to bypass endpoint detection mechanisms. The malware operates primarily in memory, minimizing disk artifacts, and employs advanced anti-VM technology to evade sandboxes and analysis labs. PDFSIDER features a robust cryptographic implementation using the Botan library for secure communications. It gathers system information and provides attackers with an interactive, hidden command shell for remote execution. The malware's characteristics align with APT tradecraft, suggesting its use in cyber-espionage operations. Distribution occurs through spear-phishing emails containing ZIP archives with legitimate-looking executables.